Radar backscatter at 50 MHz from the summer polar mesosphere is sometimes much stronger than the scatter from other latitudes at any time or from polar latitudes in other seasons. Kelley and Ulwick [1987> suggested that heavy water cluster ions in this uniquely cold region of the atmosphere could be responsible because, in the presence of these ions, the enhanced, turbulence-driven spectrum of the ionization irregularities could extend to considerably shorter wavelengths than that of the neutral turbulence itself. Here we explore this idea further and relate it to past and planned incoherent scatter measurements at EISCAT. These observations should be able to establish whether or not water cluster ions have an anomalously low diffusion coefficient. ¿ American Geophysical Union 1987